The invention is in the field of hydraulic equipment. More particularly, the invention is a hydraulic cylinder designed to inwardly contain major portions of its control system. The cylinder furthermore includes a unique internal structure that optimizes the functionality of the unit.
Hydraulic systems are often employed in machines that are used in harsh environments and must therefore be reliable and preferably require a minimum of maintenance. Examples of such equipment are backhoes and front-end loaders. In machines of this type, the hydraulic systems are sized and designed to give the machine the capacity to accomplish work that requires the application of significant amounts of power.
The above-described systems typically include a large-horsepower diesel engine that can both propel the machine and drive a high-capacity hydraulic pump. The operator of the machine controls the operation of the machine""s hydraulically-actuated components through the use of valves that affect the flow of hydraulic fluid to said components. In this manner, pressurized fluid is selectively directed to linear actuators, in the form of hydraulic cylinders, to accomplish the required work.
The application of pressurized fluid to a hydraulic cylinder in a predetermined manner will cause the cylinder""s inwardly-contained piston to move within the body of the cylinder. As a result, the piston rod attached to the piston will be either extended from, or retracted into, the cylinder to cause the desired movement of the machine""s member(s) attached to the cylinder.
In typical hydraulic systems, the control valve that is responsible for the operation of any particular hydraulic cylinder is located at a distance from the cylinder. Long flexible hoses and pipes are then used to connect the control valve to the cylinder and to a source of pressurized fluid. Another set of hoses and pipes will usually also be employed to provide a flow path for returning fluid to a reservoir, also known as a sump. Depending on the complexity of the system, additional hoses may be employed between main and pilot valves and between system check valves and the control and/or pilot valve(s).
One problem with prior art hydraulic systems is that by the time the pump, reservoir, and all the different valves and hydraulic cylinders are connected together, the end result is a large number of hoses, fittings and pipes located in damage-prone areas. The hoses are susceptible both to punctures and to environmental degradation.
Another problem with prior art hydraulic systems is that not only are the hoses prone to being damaged, all of the different components and hoses are connected together by fittings that are subject to leakage. Leakage problems are exacerbated when the equipment is being used in an environmentally-sensitive area where any leaked hydraulic fluid must be recovered along with any contaminated soil. In this manner, even minor leaks pose safety and maintenance problems.
In some hydraulic systems, the use of connecting hoses is minimized by mounting the hydraulic cylinder""s control valve directly onto the side of the hydraulic cylinder. However, this results in the control valve being located in an exposed area where it can be damaged by falling debris or by accidental contact with external structure or formations.
The invention is a hydraulic cylinder having a design optimized for durability, convenience and overall low cost. The cylinder may be employed in almost any machine in which a hydraulic cylinder is required. The invention is especially useful for employment in machines subject to harsh usage and environmental conditions, such as earth-working machinery including front-end loaders, bulldozers, etc.
A hydraulic cylinder in accordance with the invention is similar in outward appearance to most standard hydraulic cylinders. However, the head portion of the cylinder, also known as a cylinder head, includes the cylinder""s main control valve. The cylinder head preferably further includes one or more electrically-actuated pilot valves and other ancillary components required to control fluid flow to the cylinder, such as one or more pilot-operated check valves.
Like prior art hydraulic cylinders, the cylinder in accordance with the invention is elongated in shape and includes a movable piston attached to one end of a piston rod. However, to optimize the performance of the valve and to make best use of the above-described structure of the cylinder head, a fluid transfer tube and hollow piston rod are employed within the cylinder. The tube extends from the cylinder head through the center of the piston and into the interior of the piston rod. The piston rod features at least one port located near the piston to enable fluid flow between the interior area of the piston rod and the interior area of the cylinder surrounding the piston rod. This creates an internal fluid path that extends from the cylinder head, through the transfer tube, through the interior of the piston rod, and then into the area of the cylinder surrounding the piston rod. In said area, the fluid can apply pressure to a bottom surface of the piston. In the prior art, this transfer tube is located outside the cylinder and is therefore subject to being damaged.
The cylinder head additionally includes a port through which fluid can be transferred directly from the cylinder head to an area located within the cylinder and in front of the piston. When fluid is selectively diverted into this area, the fluid can apply pressure to the top surface of the piston. The fluid flow to the above-noted port or to the transfer tube is controlled by the main control valve.
In the preferred embodiment, the main control valve is a spool-type valve controlled by two pilot valves. Both pilot valves are also located in the cylinder head. Each pilot valve is preferably electrically actuated via a solenoid. The solenoid for each pilot valve is also preferably located within the cylinder head in a location where it is easily serviceable.
The electrical wiring to the solenoids extends out of the cylinder head and is operatively connected to a remotely-located control switch. In this manner, electrical actuation of the control valve structure may be achieved by an operator through actuation of a switch.
In the preferred embodiment of the invention, the hydraulic fluid return line/hose inwardly contains the wires that connect the solenoids to the operator-actuated control switch. This minimizes the number of components of the system exposed to the external environment.
To ensure the desired direction of fluid flow, the cylinder head preferably also includes two pilot-operated check valves. The first of said valves is in the fluid path leading to the cylinder area in front of the piston, i.e.xe2x80x94the area located between the piston and the cylinder head. The other of said valves is in the fluid path that leads to the area behind the piston, i.e.xe2x80x94the area of the cylinder surrounding the piston rod. Preferably, when one pilot-operated check valve is opened to allow the flow of pressurized fluid to the cylinder, the other pilot-operated check valve will also be opened to provide a return path for fluid displaced from the cylinder. Also in the preferred embodiment, each of the pilot-operated check valves can be fluid locked into a closed position to maintain the piston in a stationary position when the control valve is in a neutral condition.
By encasing the hydraulic cylinder""s main control valve and other fluid-related components within the cylinder head, the components are protected from damage. Furthermore, the number of hoses and fittings required for the hydraulic system are significantly reduced. As a result, the invention provides a hydraulic cylinder that avoids most of the problems of the prior art. Furthermore, the hydraulic cylinder has a shape and space envelope similar to most conventional units. In many cases, this allows the invention to be substituted for a conventional unit.